1. Field of the Invention
The present invention relates in general to internal combustion engine control systems and, specifically, to an internal combustion engine control system for modifying pedal progression with acceleration feedback.
2. Description of the Art
The accelerator pedal in an automobile must read the intent of the driver to: (1) accelerate the vehicle; (2) maintain vehicle speed (i.e., neither accelerate nor decelerate the vehicle); and (3) decelerate the vehicle. Moreover, the pedal must provide position feedback to the driver. Currently, these functions are performed through an electronic throttle control, which uses a simple pedal to throttle position progression table. When the accelerator pedal is displaced, the angle of the throttle is increased by a throttle actuator. This allows more air into the engine and thereby increases engine power. The spring load of the pedal changes at each pedal position, providing feedback to the driver.
Current electronic throttle control produces excessive variations in throttle position and speed for a given pedal displacement as terrain, altitude, gear, axle or vehicle load change. Further, the current method cannot predict the vehicle speed intended by the driver. Cruise control systems can also be used to accelerate or decelerate the vehicle or to maintain vehicle speed. However, such systems require hardware beyond that needed by the electronic throttle control.
The present invention is a method and apparatus for controlling the throttle position of an engine by modifying the current electronic throttle control. The invention makes changes to the throttle position using the driver""s intended acceleration and speed, instead of using the current pedal progression that directly changes throttle position based on accelerator pedal displacement.
Specifically, the method starts by measuring the displacement of an accelerator pedal and the current speed of the vehicle. Using a table lookup function incorporating pedal displacement and the current vehicle speed, the driver""s target acceleration is determined. A second table lookup function is used to determine the driver""s intended end vehicle speed, which is the speed the driver would reach if the accelerator pedal remained at its measured displacement. Then, a desired throttle position is calculated using an acceleration-based rate of change. Preferably, a standard arbitration is performed with signals from other engine control systems. If the other systems do not indicate a need to limit changes to the throttle position, the throttle is adjusted to the desired throttle position.
The apparatus of the present invention comprises means for measuring the displacement of an accelerator pedal and the current speed of the vehicle. It also comprises a table lookup function incorporating pedal displacement and the current vehicle speed to determine the driver""s target acceleration. A second table lookup function determines the driver""s intended end vehicle speed. The apparatus also includes means for calculating a desired throttle position using an acceleration-based rate of change and means for performing a standard arbitration using signals from other engine control systems. Finally, the apparatus contains means for adjusting the throttle to the desired throttle position, which adjustment will occur if the other systems do not indicate a need to limit changes to the throttle position.
In one aspect of the invention, the desired throttle position is the output of a PID controller using as its input the difference between current vehicle speed and the end vehicle speed and a gain using the acceleration-based rate of change.
In one aspect of the invention, the acceleration-based rate of change is the driver""s target acceleration. In another aspect of the invention, the acceleration-based rate of change is another engine parameter calculated from the driver""s target acceleration, such as torque.
The present invention automatically regulates acceleration, and thus vehicle speed. This allows tracking to a target acceleration and maintaining vehicle speed at points of zero acceleration using a simple and direct interface to determine driver intent. The invention allows the driver to maintain a desired vehicle speed at a comfortable pedal position regardless of terrain, altitude or vehicle loading conditions without requiring a cruise control system. Finally, the invention accurately determines the end vehicle speed, which can be used as an input into other engine control systems such as for future enhancements in transmission shift scheduling.